New Results from Ground-Based Transit Spectroscopy Observations  

Jacob Bean

Harvard-Smithsonian CfA

University of Chicago

A new technique for ground-based transit spectroscopy

Observation strategy:

•Time-series spectroscopy with multi-object spectrographs during transits/occultations

•Simultaneous spectra of target and multiple reference stars during transits – “differential spectroscopy”

•Wide slits of 12” eliminate slit losses

Goals…

•Reveal the bulk composition of the planet.

•Resolve the tension between conflicting results.

submitted to ApJ and available on astroph

New Results for GJ1214b:

• New spectroscopy in J, H, and K simultaneously (Magellan + MMIRS)

• New spectroscopy 0.61 – 0.85 μm (VLT + FORS)

• New narrow-band photometry at 2.09 μm (VLT + HAWKI)

• Re-analysis of previously reported spectroscopy 0.78 – 1.00 μm (VLT + FORS)

submitted to ApJ and available on astroph

New Results for GJ1214b:

NIR Spectroscopy of GJ1214b

107 photons per exposure in K-band

50 ppm on the transit depth

GJ1214

NIR Spectroscopy of GJ1214b

K-band data

NIR Spectroscopy of GJ1214b

Parameter decorrelation

NIR Spectroscopy of GJ1214b

NIR Spectroscopy of GJ1214b

443 ppm per minute

3.4 times the photon noise

NIR Spectroscopy of GJ1214b

652 ppm per minute

6.0 times the photon noise

NIR Spectroscopy of GJ1214b

608 -- 1060 ppm per minute

2.5 times photon noise

Optical Spectroscopy of GJ1214b

504 – 1432 ppm per minute

1.3 times the photon noise

Broadband data for GJ1214b

Broadband data for GJ1214b

Our new measurements

Broadband data for GJ1214b

Re-analyzed previous measurement

Broadband data for GJ1214b

Spitzer data (Desert et al. 2011)

Broadband data for GJ1214b

Croll et al. (2011) measurements

Broadband data for GJ1214b

• No spectral features detected

• Croll et al. (2011) K-band point inconsistent with MMIRS broadband point at 4.1σ

Broadband data for GJ1214b

• No spectral features detected

• Croll et al. (2011) K-band point inconsistent with MMIRS broadband point at 4.1σ

• Solar composition model in chemical equilibrium ruled out at 7.9σ

• Solar composition model with methane removed is ruled out at 5.2σ

K-band spectroscopy for GJ1214b

• No spectral features detected

• Confirm results of Crossfield et al. (2011) at lower resolution

K-band spectroscopy for GJ1214b

• No spectral features detected

• Confirm results of Crossfield et al. (2011) at lower resolution

• Solar composition model in chemical equilibrium ruled out at 4.3σ

• Solar composition model with methane removed is consistent

• No spectral features detected

Optical spectroscopy for GJ1214b

• No spectral features detected

• Solar composition model in chemical equilibrium ruled out at 6.6σ

• Solar composition model with methane removed ruled out at 5.2σ

Optical spectroscopy for GJ1214b

Summary:

GJ1214…

•A remarkably complete ground-based spectrum

•Spectrum is flat, no deeper transit in the K-band

•Atmosphere is either >70% water, or has high-altitude clouds/haze

Results for other planets with the same technique coming soon

Observation schematic

spectrum

12” x 30” slits

Appro

x 5’